CHM 333

Exam One

9/30/98

Dr. Foy

 

You have just been named to the weapons inspection team from the U.N. As the lead chemist on the team, it is up to you to set sampling protocols, statistics, comparison of different tests, and corrections for massing of samples.

One of the indications of explosives is a trace amount of phosphate. While explosives are "legal", phosphates can also be tied to some biological warfare weapons as well. One of your many tasks as a weapons inspector is to identify the amount and purity of phosphates since both measures give clues as to which weapons are being manufactured.

 

1 a. The first problem that you are presented with is the sampling of 45-50

gallon drums of a powder which is thought to contain some amount of phosphate. You can only perform 50 analyses. Develop an ideal sampling scheme.

b. The leader of the team has just informed you that you are moving to a new site in 15 minutes and this means you can only perform 5 analyses - adjust your procedure.

 

2. The last phosphate concentration was reported in terms of 1.41 x 10-6 g/mL, and International standards require that you report in terms of:

 

molarity, ppm, molality, and % mass

 

3. In weighing out standards, your technicians have collected the data below. Find and report the following:

standard deviation

relative STD assuming the true mass is 1.500g

 

Trial One

Trial Two

1.499

1.501

1.498

1.502

1.501

1.499

1.503

1.498

1.510

1.503

1.489

1.502

1.488

1.504

1.491

1.497

1.492

1.498

1.493

1.495

 

4. The International Committee is concerned that you are not using an appropriate scale, and that you haven't considered the difference in density. You quickly sketch a diagram of your electronic balance and correct the average weight for buoyancy dair = 0.0011g/mL.

 

 

 

5. To assure accuracy you have used two different methods for phosphate analysis. Prove whether or not the methods are statistically the same or significantly different.

 

Method 1 (ppm) Methods 2 (ppm)

1.0021 1.0006

1.0001 1.0075

1.0101 1.0011

1.0121 1.0023

1.0000 1.0201

1.0331 1.0033

 

 

 

6. One of the International Committee members is a closet chemist and suggests trying to precipitate phosphate as a calcium salt to determine purity

 

a. you quickly calculate the concentration of calcium needed to begin precipitation

Ksp = 1.4 x 10-13

b. If the difference between explosive phosphate and bio-phosophates is 1g/L explosive and 1mg/L bio, and the mechanisms of precipitation are completely different, is the separation possible?

c. We know that the desired reaction is exothermic. Using thermodynamics (equation) show what to do about temperature.